Refining of fatty oils and fats



United States Patent REFINING 0F FATI'Y OILS AND FATS Frank E. Sullivan,Staten Island, N. Y., assignor to The De Laval Separator Company,Poughkeepsie, N. Y., a corporation of New Jersey No Drawing. ApplicationMarch 5, 1952, Serial No. 275,037

3 Claims. (Cl. 260425) This invention relates to the refining of fattyoils and fats, particularly vegetable oils and fats, with the use ofcaustic soda as a refining agent. It has for its principal object theprovision of an improved refining process of this character for removingfree fatty acids from the material, with a smaller refining loss thanhas been possible heretofore.

Crude vegetable and animal oils and fats are commonly refined withcaustic soda in order to remove free fatty acids, coloring matter andnon-glyceride impurities. In the conventional caustic soda refiningmethod, the oil is treated with fairly strong lye and intimately mixed,the lye reacting with free fatty acids and any phosphatides present toform soap. The resulting soapstock or foots is removed from the refinedoil by settling or centrifuging.

The difiiculties encountered in caustic soda refining are principallythose of entrainment of neutral oil in the soapstock and saponificationof neutral oil by the lye, both of these resulting in high refininglosses, which are very undesirable. In certain non-phosphatidic oils,entrainment is due principally to the soaps formed during the refiningoperation, while in phosphatidic oils, such as corn oil, soybean oil andcottonseed oil, the soaps are also aided by the phosphatides inemulsifying or entraining the neutral oil.

I have found that when intimately mixed, phosphoric acid reacts withvarious components in crude vegetable oils and fats (which are hereregarded as oils) to form a complex addition compound with thephosphatides present in the crude. I have further found that thereaction compounds thus formed will then react with the refining lye orcaustic soda in the conventional neutralizing process, thereby formingde-emulsifying agents concurrently with the neutralization of the fattyacids, which results in lower refining losses.

My tests have shown that the intimate mixture of crude vegetable oil andsmall amounts of phosphoric acid requires less than the calculatedamount of sodium hydroxide or lye to neutralize the fatty acids andphosphoric acid present in the mixture (the calculated amount of NaOHbeing that normally expected to react with the fatty acids plus theadded phosphoric acid in the mixture). This indicates that thephosphoric acid is at least partially reacted with the phosphatidiccompounds present in the crude oil. The addition compounds of thisreaction then have a very important efiect on the formation of the soapin the ensuing neutralization step, in that they cause a liqueficationof the soapstock and, by their buffer action, tend to reduce thesaponification of the neutral oil while at the same time lowering theamount of occluded neutral oil in the soapstock. This treatment thuspermits more complete separation in the centrifuges used for separatingthe soapstock from the oil, giving an overall decrease in the refiningloss.

The amount of phosphoric acid required in the new process is small, theamount on a full strength basis being in the order of 0.1% to 0.4% byweight of the crude oil. Thus, when using a standard commercial 75%solution of phosphoric acid, amounts in the order of 0.13% to 0.53% byweight of the crude oil are required. Generally, the equivalent of fullstrength of phosphoric acid in an amount of about 0.2% by weight of thecrude oil is suflicient for most purposes. The phosphoric acid is addedto and intimately mixed with the crude oil prior to the introduction ofthe refining lye, so that the addition compounds of the reaction areformed by the time ice the lye is added. The lye is preferably added inan amount which is only slightly in excess of that theoreticallyrequired (the stoichiometric amount) for neutralization of the freefatty acids in the oil, an excess of 0.1% to 0.5% of sodium hydroxidebeing preferred. The latter may be added continuously to a stream of theoil after the phosphoric acid and oil have been thoroughly mixed. Therefining lye is thoroughly mixed in the oil and phosphoric acid mixture.The resulting mixture of oil and soapstock is then passed to acentrifugal separator at an emulsion-breaking temperature, usually 6080C., so that the soapstock is continuously separated from the refinedneutral oil. The centrifuge maybe of any conventional type used forseparating soapstock from oil.

The following are specific examples of the practice of the invention:

Example 1 To a batch of crude cocoanut oil, 0.2% (by weight) of asolution of phosphoric acid was added, and the entire mass was wellagitated and heated to 60 C. This mixture was then pumped through a highspeed mixer, at which time the refining lye (NaOH) was continuouslyproportioned into the flow of the mixture of crude oil and phosphoricacid. The refining lye was continuously added to the mixture in theproportion of 11.7% by weight, using 12 B. lye (which is a 0.1% excessof NaOH over the theoretical amount required to neutralize the freefatty acids). The refining mixture was heated to 70 C. while flowingthrough the high speed mixer and was then fed continuously to acontinuous centrifugal separator, where the soapstock was removedcontinuously from the refined neutral oil. The refining loss on a drybasis was 6.3%. The crude cocoanut oil had a free fatty acid content of6.0% and an absolute Wesson loss of 6.3% on a dry basis. A refining lossequal to the theoretical loss of the crude oil was obtained.

Example 2 To a batch of crude cocoanut oil with a free fatty acidcontent of 6.6%, 0.15% (by weight) of a 75% solution of phosphoric acidwas added with sufiicient agitation to insure an intimate mixture. Theentire mixture was heated to 60 C. and was then refined by the proceduredescribed in Example 1. The amount of lye used was 13.9% (by weight) of12 B. sodium hydroxide (which is a 0.12% excess over the theoreticalamount required to neutralize the free fatty acids), the lye beingproportioned continuously into the crude oil-phosphoric acid mixture.The refining loss on a dry basis was 6.9%. The crude cocoanut oil had anabsolute Wesson loss of 6.8% on a dry basis. A refining loss wasobtained which was very close to the theoretical loss of the crude oil.

Example 3 A crude peanut oil at 30 C. was continuously proportioned orfed to a high speed mixer, at which time a small amount of a 75%solution of phosphoric acid (0.2% by weight) was continuously fed intothe oil and intimately mixed with it. The crude oil-phosphoric acidmixture, after emerging from the mixer, was fed to a second high speedmixer, where the refining lye was continuously proportioned into thecrude oil-phosphoric acid mixture in the amount of 8.4% of 12 B. lye(0.36% excess NaOH over the theoretical amount required to neutralizethe free fatty acids). The entire intimate mixture was heated to 60 C.for a break and then fed to a continuous centrifugal separator. Therethe soapstock was continuously separated from the refined neutral oil.The refining loss, on a dry basis, was 6.5%, while the AOCS cup loss was8.1% on a dry basis. The absolute Wesson loss was 5.5% on a dry basis. Areduction of 20% in cup loss was obtained, or, based on the Wesson loss,a ratio of 1.19 times Wesson loss. This particular peanut oil was ofvery poor quality and had a very high phosphatide content.

Example 4 A small amount of 75% phosphoric acid (0.1% by weight) wascontinuously added to a continuous stream of heated crude cottonseed oil(FFA 20) at a temperature '6: E C, in such a manner as to form anintimate Triix't'ur'e. Sodiurnliydroxide inthe'form of 16 'B. lye,

using 0.4% excess as NaOI-I, was accurately proportioned in a.continuous manner into the crude cottonseed oil Fco'nfainingthephosphoric acid. The-mixture was then 'to -sparate' the refinedoil fromthe soapstock. The soa stock 'was discharged continuously as a dark,very fluid material. The resulting refining loss was 4.5% on a'drybasis. The'cup-loss'was 9.0% on a dry basis. The reductioninrefining loss was 50%.

1. In the refining of fatty oils, wherein caustic soda is 'niix'edWithEthe crude .oil 'to neutralize the free fatty "acids therein, and inwhich the resulting soapstock is separated fro'm the refined oil, theimprovement which c'omprisesadding phosphoric acid to the crude oil inan amount, on a full strength basis, in the order of 0.1 to 0.4% byweight of the crude oil, and reacting it with the oil to form additioncompounds prior to the mixture of the caustic soda with the oil, therebyreducing the subsequent refining'loss'es, an'dthe'n 'iiit'roducin'gtfiecaustic soda into the mixture and centrifuging the mixture at anemulsion-breaking temperature.

2. The improvement according to claim 1, in which the caustic soda isadded to the oil in an amount approximating the theoretical amountrequired to neutralize the free fatty acids in the crude oil.

3. The improvement according to claim 1, in which the caustic soda isadded to the oil in an amount approximating 01-05% in excess of thetheoretical amount required to neutralize the free fatty acids inthecrude oil.

References Cited in the file oif this patent UNITED STATES PATENTS

1. IN THE REFINING OF FATTY OILS, WHEREIN CAUSTIC SODA IS MIXED WITH ACRUDE OIL TO NEUTRALIZE THE FREE FATTY ACIDS THEREIN, AND IN WHICH THERESULTING SOAPSTOCK IS SEPARATED FROM THE REFINED OIL, THE IMPROVEMENTWHICH COMPRISES ADDING PHOSPHORIC ACID TO THE CRUDE OIL IN AN AMOUNT, OFFULL STRENGTH BASIS, IN THE ORDER OF 0.1 TO 0.4% BY WEIGHT OF THE CRUDEOIL, AND REACTING IT WITH THE OIL TO FORM ADDITION COMPOUNDS PRIOR TOTHE MIXTURE OF THE CAUSTIC SODA WITH THE OIL THEREBY REDUCING THESUBSEQUENT REFINING LOSSES, AND THEN INTRODUCING THE CAUSTIC SODA INTOTHE MIXTURE AND CENTRIFUGING MIXTURE AT AN EMULSION-BREAKINGTEMPERATURE.